I don't recall the detail but from sometime in the mid to late sixties, there was a regulation about not having the crankcase venting to the atmosphere. So all the classic sports cars I've had, have had close circuit venting, apart from (strangely), the Rover V8 in the MGB which has a rear breather from the crankcase, through a filter (a fuel filter actually), with an inverted U bend on the top. This was a standard fitting by the factory.
So fathom that out if you can.
